1. Field of the Invention
This invention relates to a spindle motor suitable for driving a disk for such as hard disk drive.
2. Conventional Art
FIG. 5 shows a sectional view of the gist of a spindle motor for driving a disk of an information recording medium such as a hard disk drive. This spindle motor is formed by making a hub 1 i.e. a rotor as a disk face. Further, it comprises a rotary shaft la formed in a unitary manner with the hub 1, and on the inner wall of the hub 1's outer circumference cylinder portion a magnet 2 is mounted. The rotary shaft 1a is supported on a frame 4 through two bearings 5 (radial ball bearing). At a position opposing to the magnet 2 of the frame 4, a stator 3 is fixed, which supports a coil 3a. The above spindle motor is a so-called a "shaft rotation type" of spindle motor in which the hub 1 and the rotary shaft 1a are supported by the bearing 5 and rotate in a unitary manner.
In the information recording medium, in order to carry out reading and recording correctly, it is indispensable to form a mechanism in which a head as a recording and reading means can trace a track of a disk. Accordingly, to a spindle motor to drive a disk a high precision of rotation is required. Further, also in order to secure an anti-shock, it is necessary to have a sufficient rigidity. As one of countermeasures, it has been in general to use two bearings 5 for pivoting the rotary shaft 1a of the hub 1.
Further, in order to carry out positioning at the time of an assembling process for two bearings 5 on the spindle motor correctly, a spacer 8 is disposed between the bearings 5. Since this spacer 8 is disposed in such a manner as it abuts to the outer race 5a of two bearings 5, between inner races 5b of the two bearings 5 spacing corresponding to the thickness of the spacer 8 is formed. This spacing contributes to give a preload to the two bearings 5. Such preload is, by giving to the inner race 5b of the two bearing 5 a given preload in such a manner as these come close each other, adapted to press the inner race 5b, ball 5c, the outer race 5a and the spacer 8 with each other to absorb a minute play of the bearing 5 which is inevitably generated at the time of working it precisely. Accordingly, by giving preload the rotation precision of the spindle motor is further increased and further suitable as a spindle motor for driving a disk. Further, FIG. 6 shows an example in which a spacer 4a is formed with the frame 4 in a unitary manner.
That is, as one means so as to secure the rotation precision and the rigidity of the spindle motor, it is quite effective that the spacer 8 or 4a are provided between the two bearings 5. However, such a structure has been a hindrance from the viewpoint that the height of the spindle motor is to be made lower (that is, to promote to make the spindle motor miniaturized).
Although the miniaturization of the spindle motor is a times demand, in order to attain the object, if the spacer 8 or 4a is omitted, the inner race each other and outer race each other of the bearing 5 are contacted close to make impossible to give preload. Accordingly, a minute play of the bearing 5 which is inevitable for working precision can not be absorbed to cause the rotation precision of the spindle motor to be lowered. Further, in order to make the bearing 5 itself, it has been possible to replace the bearing 5 with sintered and oil impregnated bearing or thrust ball bearing, but it has been difficult to secure a given rotation precision.
The present invention is to provide a spindle motor, and the object of the present invention is, while securing a rotation precision and rigidity, to promote to miniaturize the spindle motor.
In order to solve the above problem, according to a first aspect of the present invention, two bearings are disposed while abutting each other between a rotation shaft and a frame, wherein, without disposing a spacer, spacing at least between the outer races or the inner races is formed to make use of said spacing for giving preload to the bearing.
Generally, in the outer and inner races, since high precision has to be secured in high precision in sizing, by abutting two bearings a precision of assembling two bearings is secured. In thus abutting status, when making spacing between the outer races or the inner bearings, because any spacer is not disposed between bearings, the height of the spindle motor is held low. And, when assembling the spindle motor, if a preload force is applied to a race (outer or inner race) which has the aforementioned spacing, a tiny displacement caused by the preload become possible to absorb the minute play inevitable to the bearing to increase the rotation precision of the spindle motor after completion.
Further, according to a second aspect of the spindle motor of the present invention, in a shaft rotation type of spindle motor, between the rotation shaft and the frame, two bearings the inner race of which is narrower in width compared with the outer race are disposed, the end face of each outer race is made to abut, and each end face of the inner race is given by a preload.
According to the present invention, by abutting of each end face of the outer race of the two bearings, spacing is formed between the inner races each other due to a narrower width compared with the outer race. As mentioned above, the outer race and the inner race of the bearing are secured high in size precision, so that, due to the abutting of the end face of the outer races, the assembling precision between two bearings is secured. Further, the spacing formed between the inner races enables the inner race to displace minutely due to giving a preload to the end face of the inner race at the time of assembling the spindle motor, thereby it is intended to absorb a tiny play inevitable to the bearing and increase the rotation precision after completion of the spindle motor.
Further, according to third aspect of the spindle motor of the present invention, in the shaft rotation type of spindle motor, between the rotation shaft and the frame, two bearings the outer race of which is narrower in width compared with the inner race are disposed, the end face of each inner race is made to abut, and each end face of the outer race is given by a preload.
According to the present invention, by abutting of each end face of the inner race, spacing is formed between the outer races each other due to a narrower width compared with the inner race. As mentioned above, the outer race and the inner race of the bearing are secured high in size precision, so that, due to the abutting of the end face of the inner races, the assembling precision between two bearings is secured. Further, the spacing formed between the outer races enables the outer race to displace minutely due to giving a preload to the end face of the outer race at the time of assembling the spindle motor, thereby it is intended to absorb an tiny play inevitable to the bearing and increase the rotation precision after completion of the spindle motor.
Further, according to a fourth aspect of the spindle motor of the present invention, merely one of two bearings is provided with a difference in width between the inner race and outer race in width, due to such construction too, when the outer race abuts each other, spacing between the inner races is formed, or when the inner race abuts each other, spacing between the outer races is formed. Accordingly, the function as well as the above can be affected
Further, according to a fifth aspect of the spindle motor of the present invention, it is what is made by replacing the spindle motor in any one of aspects 2 to 4 with the shaft fixation type of the spindle motor, and according to a sixth aspect of the spindle motor of the present invention, the spindle motor is formed by separating the rotation shaft and the hub.